Hardwood Floors and Humidity

If you have hardwood floors and humidity in your home is not within the the optimal range of 35-55%, your floors may be at risk. Wood is a porous material, and humidity levels have an impact on appearance and durability of your hardwood floors. A lack of moisture in the air, or low relative humidity, during the winter months, causes a loss of moisture in the wood, resulting in shrinkage, splintering or splitting along the grain, which damages the finish. Hardwood naturally shrinks and expands with seasonal moisture changes. This can often cause the boards to permanently lose their shape (rising at the edges) or create gaps between the boards, that causes them to squeak. Should the wood finish become damaged, regular maintenance will become an issue.

Also, if the humidity levels are too high, you run the risk of too much moisture seeping into the wood. This could cause the boards to swell, which could lead to warping or cupping. Both solid hardwood and engineered hardwood floors are susceptible to moisture damage.

What can be done about this?

Firstly, select the correct floor. Solid hardwood floors do not perform well if they are installed over concrete (i.e. in basements or condominiums). Concrete tends to accumulate moisture, which can then be absorbed by the wood, causing dimensional changes and squeaky floors.

Solid sawn and engineered flooring are more stable than solid wood and are most suitable for these areas. Some warranties specify 35 to 55 percent relative humidity, or 40 to 60 percent relative humidity, as the acceptable range. As long as the humidity does not fall below the minimum range, no gaps will appear between the planks. It is important to check the individual manufacturer’s recommendations and warranty. Not complying with the manufacturer’s recommendations can result in the warranty being voided.

Wide boards will shrink more than narrow boards for a given change in moisture content. A 5 inch wide plank will shrink twice as much as a 2 1/4 inch strip, resulting in gaps twice as large between 5 inch boards. More joints create the possibility for more gaps to be distributed over a given area.

Some wood species tend to be more dimensionally stable than others. For example, for a given change in moisture content, there will be more shrinkage in a 5-inch wide hickory plank than a Red Oak or American Walnut plank, while Brazilian Walnut (Sukupira), Brazilian Tik (Camru) or Brazilian Cherry (Jatoba) will tend to lose their moisture more quickly.

For the same amount of moisture change, quarter sawn flooring shrinks about half as much flatsawn flooring, and will have smaller gaps.

Quarter sawn floors are available mostly in unfinished form, and require finishing at the job site. Floor finishing allows for greater colour selection, and for the maintenance of a groove-free appearance.

So, regardless of the wood species, structure or cut, there should always be an efficient humidifier in place throughout the heating season. The recommended manufacturer moisture level and optimal temperature of 22 degrees Celsius should be maintained year round to ensure the longevity and performance of your floor. It is important to ensure that the humidity controls are functional before the floors are installed.

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